This invention relates to the control of water quality in a rinse tank, such as the tanks which are widely used in electroplating plants. In the simplest form of rinse tank, clean water is continuously introduced at one side of the tank, with an overflow line at the opposite side of the tank. However this procedure results in considerable waste of water since water flow is not related to water quality. Control systems are in use today which measure the electrical conductivity of the water and add clean water only when the conductivity increases above some preset figure, with the conductivity being related to the contaminants in the rinse water.
These prior art systems utilize a conductivity cell with fixed configuration positioned in the water and an electronic circuit separate from and connected to the cell for providing the control if the inlet water valve. The conductivity set point for turning on the water supply is adjusted in the electronics. Because of the severe chemical and electrical conditions in the environment of most industrial electroplating plants, the desired stability and precision of operation has been achieved only by resorting to expensive and complex electronics and cell materials.
Accordingly, it is an object of the present invention to provide a new and improved control system for a water rinse tank of the like. A particular object is to provide a new and improved conductivity cell for use with such a control system, with a cell configuration that is adjustable to provide operation over a wide range of set points. A further object is to provide such a system in which the electronics can be incorporated in the cell structure for positioning within the tank providing improved environmental stability without complex circuitry and requiring only two nonpolarized, unshielded wires as a cable from the cell. Another object of the invention is to provide a new and improved control circuit for use with the conductivity cell with the circuit providing substantially the same ideal waveform at the cell irrespective of line voltage and frequency irregularities thereby insuring that the cell always operates under the same optimum conditions regardless of contamination of the cell surfaces.